The present invention relates to black pigments, and particularly black pigments useful for glass enamel coloring.
Increased governmental requirements, particularly in Europe, regarding the recycling of automobiles and automobile parts, have placed pressure on automotive glass manufacturers to develop windshields and other glass parts that can be easily recycled. This pressure has, in turn, been passed on to pigment manufacturers whose pigments constitute a significant portion of the problems in the recycling process. Specifically, even small amounts of certain transition metal impurities (for example, vanadium, chromium, cobalt, nickel and copper) can color the recycled glass, greatly reducing its market value. Since automobile glass is generally a black enamel which incorporates black pigments, it is desirable to have a black pigment which does not include those transition metals in order to minimize the recycling problems which occur at the end of an automobile""s life. In addition, since there may also be some health issues associated with some of those transition metal elements, there is also a substantial market for a blue-shade black pigment that is free from chromium and nickel.
Currently, most automobile black glass enamels employ copper chromite black pigment. This pigment provides satisfactory color and opacity but has the drawback of containing transition metals that will tint glass upon recycling. Strontium iron oxide (Sr2Fe2O5) is known and has been studied for quite some time as a material in the electronics industry. It exists as an oxygen deficient perovskite. Of more relevance to the present invention is the fact that its color is reported to be black and that it contains none of the undesirable transition metals for pigment applications. This same perovskite structure can also be achieved using manganese in place of iron (Sr2Mn2O5 and SrMnO3, depending on the manganese oxidation state). Variants of all three compounds are also known to exist, where calcium, barium, samarium or europium substitute for all or part of the strontium. Within this same elemental group, phases with the compositions SrFe12O19, Sr4Fe2O7-x and Sr4Fe3O10-x also exist, as well as do their solid solutions with the elements listed above.
Strontium iron oxides and strontium manganese oxides are known for a variety of uses, including use as pigments. Examples of such disclosures follow.
U.S. Pat. No. 6,416,868, Sullivan et al., issued July 9, 2002, describes alkaline earth-manganese oxides which are taught for use as pigments. The pigments are taught to exhibit high infrared reflectance characteristics and low heat buildup properties.
U.S. Pat. No. 4,388,118, Eppler, issued Jun. 14, 1983, describes inorganic black pigments made by calcining raw materials such as manganese dioxide, manganese carbonate, strontium carbonate or calcium carbonate. It is taught that this pigment produced is particularly advantageous in that it contains no heavy metals or highly toxic material and that it has low oil absorption and high tinting strength.
Strontium iron oxide or similar doped variants are also taught for use in non-pigment applications, such as in dielectric materials (see, for example, U.S. Pat. No. 6,398,977, Nakamura et al., issued Jun. 4, 2002) or oxygen ion-conducting dense ceramics (see, for example, U.S. Pat. No. 5,723,074, Balachandran et al., issued Mar. 3, 1998). In addition, U.S. Pat. No. 6,126,743, Saegusa et al., issued Oct. 3, 2000, describes a process for the production of a dielectric glass utilizing a variety of metal oxides. Finally, U.S. Pat. No. 6,332,968, Mazanec et al., issued Dec. 25, 2001, describes a process wherein a membrane of a perovskite oxide of very broad composition is used in an electrochemical reactor.
Matsumoto and Sato, Electrochemica Acta (1980), 25(5); 53943, studies a variety of strontium iron manganese oxides for use as an anode in alkaline systems for generating oxygen.
The present invention relates to a method for providing black color to a substrate material (such as a coating, paint, plastic, glass, rubber, enamel, metal, composite or ink), comprising mixing with or coating onto said substrate material from about 0.1% to about 50% (by weight of the substrate) of a pigment having a formula
AxFeyMn1-yOz
wherein A is selected from Ca, Sr, Ba, Mg, Lanthanides, and mixtures thereof;
x is from about 0.16 to about 99;
0.5 xe2x89xa6y less than 1; and
(x+1)xe2x89xa6zxe2x89xa6(x+3)
The present invention also relates to black pigment materials in a particulate form having an average particle size of from about 0.1 to about 50 xcexcm (preferably from about 0.1 to about 2 xcexcm, more preferably from about 0.5 to about 2 xcexcm) having the formula given above. Finally, the present invention relates to a pigment composition comprising from about 0.1% to about 99% of a black pigment material, having a non-electronics grade purity, and having the same formula as that given above, the balance of the composition being a carrier for said pigment. The preferred pigment composition is in the form of frits; paste; dispersion in a solvent; dry powder; flush; lake; paint or plastic concentrate; paint, plastic or resin dispersion; or beads. A wide variety of dopant elements may be included in the pigment.
All percentages and ratios provided herein are xe2x80x9cby weightxe2x80x9d unless otherwise specified. Further, all patents and other literature references cited in this patent application are incorporated herein by reference.